In a liquid crystal display device, pixels are arrayed in a row direction (X-direction) and a column direction (Y-direction). The row direction (X-direction) crosses the column direction (Y-direction). For example, gate lines parallel to the X-direction are arranged at certain intervals in the Y-direction. Further, source lines parallel to the Y-direction are arranged at certain intervals in the X-direction. The pixels are located near intersections of the gate lines and the source lines, respectively.
It should be noted that each pixel comprises a digital memory in some liquid crystal display devices. In a liquid crystal display device in which each pixel comprises a digital memory, there is no need to supply a voltage to all the source lines frequently (i.e., rewrite a pixel signal frequently), for example, in the case of displaying a still image in the entire display area of the device for a long time. In this case, power consumption of the display device can be reduced. There is no need to supply a voltage to all the source lines frequently also in the case of displaying a still image in a part of the display area and displaying moving images in the rest of the display area. In this case, too, the power consumption of the display device can be reduced because the voltage (pixel signal for moving images) should be supplied only to source lines of the rest of the display area.
In the above liquid crystal display device, however, contents of digital memories are often rewritten at the same time in each row. In such a case, for example, all the memories in the same row may be rewritten from high level to low level or from low level to high level at the same time. This level change depends on the content of a write digital video signal.
In such operation, if a number of source lines to which the write digital video signal is output have the same polarity at the same time, a significant voltage drop occurs in an output circuit that outputs the digital video signal. This may result in a data error.